Vessel collisions with bridges are increasing at an alarming rate. In the United States, rigorous design of bridges for vessel collision has been a major concern. Indeed, models have been developed to determine vessel collision forces required for designing bridge elements. What has not been adequately addressed, however, is the design of pier protection systems. Given the high number of bridge structures in navigable waterways, bridge pier protection is a serious concern.
Timber piles are key components in many existing bridge fender protection systems. Timber piles, however, suffer from a number of drawbacks including:                1) Inadequate protection for medium and high energy collisions and susceptibility to damage in low energy collisions;        2) Susceptibility to attacks by marine borers;        3) Relatively short service life;        4) Disposability problems for damaged piles that have been replaced; and        5) Environmental concerns regarding chemically treated timber that can leach hazardous chemicals into the water.        
Fiber-reinforced polymer (FRP) compositions provide alternatives to timber piles that mitigate some of the environmental hazards associated with timber piles. However, FRP piles do not provide sufficient protection against many collisions. Thus, there is a need for bridge protections systems with acceptable collision performance.
Vessel protection systems are different from typical roadside safety hardware such as vehicle crash cushions. Roadside safety hardware is primarily used to protect vehicle occupants during a crash. Vessel protection systems, in contrast, are designed to protect a bridge against excessive collision forces and, at the same time, are suppose to prevent an errant vessel from sinking or from being damaged to the point where its cargo is released into the environment. This is important because barges and vessels frequently carry cargo that could pollute and damage the environment. Another difference is that vehicle cushions are inevitably struck at high speed and must therefore fully deploy after every accident. As a result they must be repaired or reset after each impact. On the other hand, vessel protection system will be struck many times and at various speeds by floating vessels and must therefore be designed to deploy only in severe impact cases, e.g. when the applied impact force exceeds a given threshold. A third major difference between the vessel protection systems and roadside safety hardware is the type of loading that is generated. Vehicle protection systems are typically subjected to high speed impact loads generated from relatively light vehicles while vessel protection systems are typically subjected to low speed impact loads generated by heavily loaded vessels.